This invention relates to water pickup devices for watercraft and more particularly, to a unique boundary layer water pickup device which includes a curved, grooved or slotted flange with a low profile fitted against the hull of a watercraft to take advantage of the relatively constant total head of the fluid boundary layer phenomenon. The through-hull device thus facilitates a flow of water through the device into the watercraft with an amply low and fairly constant total head or pressure and with low drag at various speeds of the watercraft.
2. General Background
Water pickup devices for channeling water into a watercraft for various purposes, including cooling the engine, providing water for line bait wells, boat wash down, marine toilets, desalinators, an auxiliary generator and other marine purposes, have long been known in the art. In the common "through hull" design, the water pickup device includes a curved flange or lip which is fitted to the hull below the waterline and a threaded nipple extends from the lip through the hull, where it receives a nut for securing the device in the hull. Water pickup using this device is adequate to a speed of about 40 mph, beyond which the device fails to provide water to the watercraft interior.
One of the problems which is inherent in the operation of other water pickup devices with "scoops" in watercraft, is that of wide pressure variation in the water pickup system. This pressure varies from zero when the watercraft is at rest, to sometimes undesirably high pressures as the watercraft gains speed. Since the pressure varies widely, adequate water supply in the watercraft at a suitable working pressure is unpredictable. These devices typically extend well below the profile of the watercraft hull to deflect water into the hull and the pressure of the water being deflected by the scoop varies with the speed of the watercraft over the water.
An early such water pickup device entitled "Valve" is detailed in U.S. Pat. No. 835,854, dated Nov. 13, 1906, to G. E. Franquist. The water pickup extends well below the plane of the bottom of the watercraft for scooping the water into a vertical chamber provided with a valve for controlling the flow of water into the watercraft.
U.S. Pat. No. 1,641,670, dated Sep. 6, 1927, to G. M. French, details an "Intake" which is mounted against the bottom of the watercraft and is fitted with parallel slots and an optional, downwardly-extending flute for scooping water and channeling the water into a conduit extending into the watercraft.
A "Cooling Water Intake Apparatus For Marine Vessels" is detailed in U.S. Pat. No. 3,874,317, dated Apr. 1, 1975, to Hikita. The device includes a tubular block which is adapted to be fitted into a through-hole provided in a watercraft hull, an intake pipe removably inserted in the tubular block and a strainer provided in the intake pipe for straining the water moving through the intake pipe. A valve is also provided on the tubular block to control the rate of flow of water through the apparatus.
U.S. Pat. No. 3,878,807, dated Apr. 22, 1975, to Reskusic et al, details a "Water Intake Strainer For Use On Boats" provided on a watercraft. The strainer includes an upward-tapering housing oriented in the normal direction of travel to expose a surface of desired profile for water pickup.
U.S. Pat. No. 4,061,571, dated Dec. 6, 1977, to Philip M. Banner, details a "Marine Water Inlet Device" provided with adapters that attach to the inlet pipe and a signal apparatus that indicates when a clogging condition exists in the water circulation system of the watercraft.
U.S. Pat. No. 4,809,632, dated Mar. 7, 1989, to J. P. Hamel, details a "Bottom Scoop For Engine Cooling Water". The device includes an outer body portion secured to the outside surface of the hull of a watercraft and an inner body portion is removably disposed in the outer body portion. The inner body portion has openings in one end that admit water into a cavity in the inner body, from which cavity the water flows to the cooling system of a marine power plant.